1. Field of the Invention
The present invention relates to an image process apparatus, an image process method and a computer-readable storage medium used therein. The apparatus and method are preferably used in an image output apparatus such as a printer or the like for zooming and outputting input image information, or used in a case where low-resolution information is converted into high-resolution information in communication among plural equipments of which resolutions are different from others.
2. Related Background Art
Conventionally, various methods have been proposed as a method to convert inputted low-resolution information into high-resolution information. In such the conventional method, a conversion process method is different according to a kind of target image (e.g., multivalue image having gradation information for each pixel, binary image binarized by pseudo halftoning, binary image binarized based on fixed threshold, character image, or the like).
As a conventional interpolation method, a closest interpolation method shown in FIG. 12 to arrange a pixel value closest to an interpolation point, a common primary interpolation method shown in FIG. 13 to determine a pixel value E by a following calculation according to distances among four points (of which pixel values are assumed to be A, B, C and D respectively) surrounding an interpolation point and the interpolation point, or the like are generally used.
E=(1xe2x88x92i)(1xe2x88x92j)A+ixc2x7(1xe2x88x92j)B+jxc2x7(1xe2x88x92i)C+ijD
(in case of distance between pixels=xe2x80x9c1xe2x80x9d, distance xe2x80x9cixe2x80x9d in lateral direction and distance xe2x80x9cjxe2x80x9d in longitudinal direction from xe2x80x9cAxe2x80x9d (ixe2x89xa61, jxe2x89xa61)).
However, such a conventional art has following drawbacks.
Firstly, although the method in FIG. 12 has an advantage in a simple structure, in a case where a target image is used in a natural image or the like, since the pixel value is determined every block to be enlarged, the block is visually emphasized, thereby deteriorating image quality.
Secondly, even in a case where the method is used in a character image, linear image, a CG (computer graphic) or the like, since the same pixel values are sequentially continued every block to be enlarged, an indention phenomenon called as a jaggy phenomenon (or jag) is emphasized especially in an oblique line or the like, thereby deteriorating image quality. FIGS. 14 and 15 show states that the jag appears. FIG. 14 shows an example of input information, and FIG. 15 shows an example of resolution conversion in which the input information of which pixel number are double laterally and longitudinally by the method of FIG. 12. Generally, as a magnification becomes higher, image deterioration becomes serious (xe2x80x9c200xe2x80x9d and xe2x80x9c10xe2x80x9d in FIGS. 14 and 15 are pixels values).
On the other hand, the method shown in FIG. 13 is generally used in enlarging the natural image. In this method, the pixel values are averaged to obtain a smoothing image. However, an edge portion or a portion to which sharp image quality is necessary comes to be blurred. Further, in case of an image obtained by scanning a map or the like or a natural image containing a character portion, there is some fear that a reception side can not receive important information because of a blur caused by the interpolation.
FIG. 16 shows image information which is obtained by an interpolation process to double the input image information of FIG. 14 laterally and longitudinally in the method of FIG. 13.
As apparent from FIG. 16, the pixel values do not become uniform not only at a peripheral portion of an oblique line but also at the oblique line itself, whereby a blur appears.
Therefore, in U.S. patent application Ser. No. 311,560 filed on Sep. 23, 1994 (based on Japanese Patent Application Laid-Open Nos. 7-93531, 7-107268 and 7-105359), the applicant of this application proposed such a method as enabling to perform the resolution conversion without generating the blur caused by the interpolation process and generating the jag in forming the high-resolution information from the low-resolution information.
A basic concept of this proposal is based on a method in which components depending on the resolution are eliminated from inputted original information, the number of pixels is increased up to the number corresponding to the output resolution in such a state that the components have been eliminated, and information suitable for a new resolution is speculated and formed in such a state as the number of pixels has been increased. As a means for eliminating dependency of the input resolution, smoothing by an LPF (low-pass filter) and increasing of the pixel number can be realized by a linear interpolation. In a speculation of the high-resolution information, the pixel value to be outputted is calculated by executing different processes to the pixels classified as xe2x80x9c1xe2x80x9d and the pixels classified as xe2x80x9c0xe2x80x9d upon simply binarizing the interpolated information.
As proposed in U.S. patent application Ser. No. 715,116 filed on Sep. 23, 1994 (based on Japanese Patent Application Laid-Open No. 9-252400), there is a method for forming a satisfactory edge in which continuity of the pixel values is maintained. In U.S. patent application Ser. No. 715,116, m (mxe2x89xa71) pixels (pixel value at observation point n in m pixels is defined as P(n)) are detected from peripheral pixels of a low-resolution noticeable pixel, and an output value h(k) is calculated based on an interpolation value C(k) at each interpolation point k obtained by interpolating the noticeable pixel for plural pixels, according to a following equation.             h      ⁡              (        k        )              =                            ∑                      n            =            1                    m                ⁢                              α            ⁡                          (              n              )                                ⁢                      P            ⁡                          (              n              )                                          +              β        ⁢                  xe2x80x83                ⁢                  C          ⁡                      (            k            )                                    (                  α        ⁡                  (          n          )                    ⁢              xe2x80x83            ⁢      and      ⁢              xe2x80x83            ⁢              β        ⁡                  (                      β            ≠            0                    )                    ⁢              xe2x80x83            ⁢      are      ⁢              xe2x80x83            ⁢      arbitrary      ⁢              xe2x80x83            ⁢      coefficients        )  
However, in any of these relative applications, a basic concept is to form the edge by using maximum and minimum values within a widow on the periphery of the noticeable pixel. That is, these applications apply a method that, in a case where one noticeable pixel is enlarged N times longitudinally and M times laterally, an area within the Nxc3x97M pixels is assumed to be a part of the edge formation by the maximum and minimum values, and the pixel values of the Nxc3x97M pixels are newly calculated. According to this method, surely the original image can be converted without unnaturalness as if the high-resolution information is inputted.
However, if use of this method is expanded, there is a case where it is better to provide the image legible for a user even if impression of the original image is highly changed. For example, character information is cited as an example of this case. In a case where a printer is connected to a computer, there are a system in which the computer side having a vector-form font converts resolution into printer resolution, and a system wherein the print side having a font expands it based on code information sent from the computer side and outputs the data. In this case, since the character information has the vector form, any substantial problem does not occur even if the resolution of input and output sides are different from each other.
However, if it is assumed that the printer is connected to an equipment other than the computer, e.g., an internet television or the like, there is a case where a screen font which is displayed on a television screen and has been anti-alias processed is transmitted to the printer as it is. Further, if it is assumed that the printer is connected to the computer, there are a case where it is necessary to perform screen copy to duplicate information on the screen and a case where it is necessary to tidy and clearly output a character added to the image as a part thereof.
Such a situation is similarly applied to a facsimile apparatus which mainly treats characters and drawings. This is because, in such apparatuses, contrast is reduced and a degree of sharpness in the edge portion becomes dull according to an MTF (modulation transfer function) of an image pickup system for image reading. In these cases, it is unnecessary to generate high-resolution information by reducing the jag and interpolation blur without changing an impression of the inputted low-resolution information, but is necessary to actively convert the inputted low-resolution information into the legible image even if the impression of the low-resolution information is slightly changed. This operation depends on a fact that a property of the character information intended to be transmitted by the user is different from that of the natural image information or the like. That is, in the above equation, although the pixel value of the interpolation point is obtained by a sum of products (i.e., calculation) of the interpolation value and the peripheral pixel value, such terms as contained in the sum of products are insufficient for the calculation. That is, if the contrast of the original image is deteriorated, a high-resolution image exceeding the contrast of the original image can not be formed.
The present invention has been made in consideration of the above-described conventional problems, and an object thereof is to provide an image process apparatus, an image process method and a computer-readable storage medium used therein. In the apparatus and method, a clear high-resolution image of which contrast is higher than that of input low-resolution information can be obtained without any jag even if the contrast of the input low-resolution information is deteriorated.
Another object of the present invention is to provide an image process apparatus, an image process method and a computer-readable storage medium used therein. In the apparatus and method, an edge angle and an edge central position can be freely designed in case of converting low-resolution information into high-resolution information, thereby enabling to form a satisfactory edge having continuity.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.